共查询到20条相似文献,搜索用时 328 毫秒
1.
The inclusion of manganese-based single-molecule magnets (SMMs) into solvent cast films of poly(methyl methacrylate) (PMMA)
or polycarbonate (PC) was found to influence the thermal stability of these polymers. Examination of the thermal decomposition
profiles of PMMA films by thermo-gravimetric analysis (TGA) established that increasing weight % of SMM results in both enhancement
of the rate of decomposition initiated at “head-to-head” linkages along with suppression of the rate of decomposition initiated
at vinylidene chain ends. In the case of PC films, the temperature at which the primary thermal decomposition occurs decreases
with increasing weight % of SMM. The extent of these decomposition trends is correlated to the degree of SMM dispersal, as
studied by transmission electron microscopy (TEM). Favourable interactions between the ligands coordinated to the SMMs and
the polymer or solvent used in film preparation dictated the degree of SMM dispersal, with the ligand–polymer interactions
being dominant on the nano-length scale (1–100 nm) and ligand–solvent interactions being dominant on the micro-length scale
(>100 nm). 相似文献
2.
Dielectric and thermal characteristics of gel grown single crystals of ytterbium tartrate trihydrate
Dielectric and thermal characteristics of gel grown single crystals of ytterbium tartrate trihydrate have been carried out.
The dielectric constant has been measured as a function of frequency in the range 2 kHz–1 MHz and temperature range 30–300 °C.
The dielectric constant increases with temperature, attains a peak near 215 °C, and then decreases as the temperature exceeds
215 °C. The dielectric anomaly at 215 °C is suggested to be due to phase transition brought about in the material. The dielectric
behaviour of the material is correlated with the results on thermal analysis. Thermogravimetric and differential thermal analysis
have been used to study the thermal characteristics of the material. The experimental results show that the material is thermally
stable up to 200 °C. The decomposition process occurs in two stages until ytterbium oxide is formed at 700 °C. The non-isothermal
kinetic parameters e.g., activation energy and the frequency factor have been evaluated for each stage of thermal decomposition
by using the integral method, applying the Coats–Redfern approximation. 相似文献
3.
Hydrocarbon impurities in silicon tetrafluoride originate from the sodium hexafluorosilicate used as a precursor for the preparation
of SiF4 through the thermal decomposition of Na2SiF6. We have studied the fraction of C1–C4 hydrocarbons released as a function of temperature during the thermal decomposition of sodium hexafluorosilicate. The lighter
hydrocarbons—methane, ethane, and ethylene—are shown to be released at lower temperatures. One source of hydrocarbon impurities
in sodium hexafluorosilicate is the sodium carbonate used to prepare it. 相似文献
4.
Structure characterization of heat set and drawn polyamide 66 fibers by FTIR spectroscopy 总被引:3,自引:0,他引:3
Structural changes that occur during thermally induced and strain induced crystallization of polyamide 66 fibers were studied
by infrared spectroscopy, density measurement and optical microscopy. Two bands at 924 and 1136 cm–1 were shown to arise from the amorphous phase and assignment of the bands at 936 and 1200 cm–1 to the crystalline phase were confirmed. We demonstrated that two different infrared spectroscopic methods could be used
to determine the total crystallinity of polyamide 66 fibers. One is a calibration method in which the band ratio of 1200 and
1630 cm–1 is plotted against the crystallinity measured by density measurements. The other one is an independent infrared method. Crystallinity
obtained by the independent infrared spectroscopic method showed good agreement with crystallinity observed by density measurement.
Infrared dichroism was used to obtain the crystalline orientation using the band at 936 cm–1. The transition moment angle of 48° was found for the band at 936 cm–1 with respect to chain axis. Amorphous orientation was obtained using Stein’s equation.
Received: 18 September 2000 / Reviewed and accepted: 20 September 2000 相似文献
5.
Laser weld bonding is a new welding technology, being used to join Mg–Al alloys. The penetration depth of LWB Mg–Al joint
was larger than that in simply laser welding joint in same welding parameters. The temperature at the edge of the Al fusion
zone in LWB Mg–Al joint was higher than that in laser welding joint, which was measured through the thermal couples. The laser-introduced
plasma in LWB Mg–Al process is observed by the high-speed camera, which is different from that in laser welding process. The
surface temperature and state of the Al alloy were changed because of the addition of the adhesive, thus the laser absorptive
of Al alloy was increased in LWB process, comparing with that in laser welding process; and the decomposition of the adhesive
would make a depression in the Al fusion zone, which would be beneficial to the formation of keyhole welding in LWB Mg–Al
joint. 相似文献
6.
热致液晶聚酰胺的热分解动力学及寿命 总被引:1,自引:0,他引:1
利用热重分析法,在不同升温速率下,对热致液晶聚酰胺热分解动力学进行研究。采用Friedman、Kissinger、Ozawa以及Coats-Redfern等方法对其动力学数据进行分析说明,确定其在氮气中反应机理函数是Avrami-Erofeev法则,活化能E≈208 kJ/mol;其在空气中初始热分解反应机理函数为Mempel Power法则,活化能E≈172 kJ/mol,后期热分解反应机理函数为反Jander法则,活化能E≈111 kJ/mol。并以失重5%作为寿终指标,计算热致液晶聚酰胺在不同温度的寿命,结果表明,其在尼龙加工温度范围内不会失效,适于与尼龙进行复合加工。 相似文献
7.
The preparation of Ce(IV) oxide-based polishing powders by thermal decomposition of carbonates was studied and the effect
of the calcination process conditions on the properties of product was examined. High-grade polishing powders can be produced
at calcination temperatures 700–1200°C, the maximum polishing efficiency is achieved by calcining at 1000–1100°C. The observed
dependences were interpreted from the standpoint of the present mechanochemical theory of glass polishing. 相似文献
8.
Zhanshuang Li Yanchao Song Jun Wang Qi Liu Piaoping Yang Milin Zhang 《Bulletin of Materials Science》2011,34(2):183-189
In this paper, we describe a general process for the synthesis of highly crystalline Zn–Ni–Al hydrotalcite-like materials.
The structure and thermal decomposition of the prepared samples are studied by XRD, FT–IR, TG–DSC, SEM, TEM and N2 adsorption/desorption. The morphology of large-sized, porous and hexagonal platelike Zn–Ni–Al hydrotalcite is affected by
calcination temperature. BET specific surface area and pore volume are observed to increase with increase of the calcination
temperature up to 700°C followed by a further decrease with increasing temperature. 相似文献
9.
T. A. Kostereva Yu. N. Panov V. N. Artem’eva N. V. Kukarkina N. A. Nikanorova V. V. Kudryavtsev 《Journal of Engineering Physics and Thermophysics》2005,78(5):948-953
The time change in the melt viscosity of the polyamide composite forming at the final stage a polymer with the structure of
a semi-interpenetrative polymer mesh has been investigated. To impregnate with the composite melt the carbon fiber for forming
carbon-filled plastics, it is necessary to preserve the low viscosity of the melt for a long time. This is achieved by preliminary
heat treatment of the composite and introduction of fullerene into it.
__________
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 109–113, September–October, 2005. 相似文献
10.
G. Alarcón-Flores M. Aguilar-Frutis M. García-Hipolito J. Guzmán-Mendoza M. A. Canseco C. Falcony 《Journal of Materials Science》2008,43(10):3582-3588
Yttrium oxide thin films are deposited on silicon substrates using the ultrasonic spray pyrolysis technique from the thermal
decomposition of a β-diketonate, yttrium acetylacetonate (Y(acac)3). The decomposition of Y(acac)3 was studied by thermogravimetry, differential scanning calorimetry, mass spectrometry, and infrared spectroscopy. It was found
that a β-diketone ligand is lost during the initial steps of decomposition of the Y(acac)3. The rest of the complex is then dissociated or degraded partially until Y2O3 is obtained in the final step with the presence of carbon related residues. Then the Y(acac)3 was used to synthesize Y2O3 thin films using the spray pyrolysis technique. The films were deposited on silicon substrates at temperatures in the range
of 400–550 °C. The films were characterized by ellipsometry, infrared spectroscopy, atomic force microscopy, and X-ray diffraction.
The films presented a low surface roughness with an index of refraction close to 1.8. The crystalline structure of the films
depended on the substrate temperature; films deposited at 400 °C were mainly amorphous, but higher deposition temperatures
(450–550 °C), resulted in polycrystalline with a cubic crystalline phase. 相似文献
11.
Interphase processes in the compositions of aromatic polyamide phenylone with element-carbon fibers are studied. Significant
differences in the structure and properties of polyamide discretely reinforced with metal-carbon fibers and carbon fibers
with functional groups are revealed. It is found that the observed changes are mainly due to the physicochemical interaction
on the interface “fibrous filler-polymer matrix” during formation of the composition.
State Agrarian University, Dnepropetrovsk; Institute of General and Inorganic Chemistry, Belorussian Academy of Sciences,
Minsk. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 3, pp. 86–90, May–June, 1999. 相似文献
12.
Thermal conductivities of Ni–Cr solid solution alloys have been measured to develop a prediction equation for thermal conductivities
as functions of temperature and chemical composition. Samples used were Ni–x at% Cr (0 ≤ x ≤ 22) and commercial alloys of Nichrome Nos. 1 and 2. Thermal conductivity measurements were carried out using the transient
hot-strip method over a temperature range from 293 K to 1273 K. The thermal conductivities of the alloys increased with increasing
temperature and decreased with increasing Cr concentration at constant temperature. The Smith–Palmer equation has been examined
to relate the thermal conductivities of the alloys to the electrical resistivities. The thermal conductivity and electrical-resistivity
data, respectively, in the present work and in the literature have confirmed that the Smith–Palmer equation applies to Ni–Cr
solid solutions and Nichrome alloys. On the basis of this equation, the thermal conductivity of Ni–Cr solid solution alloys
has been expressed as a function of temperature and chemical composition. This analysis has also been applied to Ni–Fe and
Cu–Ni solid solution alloys. 相似文献
13.
V. Sorna Gowri Luís Almeida Maria Teresa Pessoa de Amorim Noémia Carneiro Pacheco António Pedro Souto Maria Fátima Esteves Sunil Kumar Sanghi 《Journal of Materials Science》2010,45(9):2427-2435
Polymer nanocomposites offer possibility of developing a new class of nanofinishing materials for textiles with their own
manifold of structure property relationship. Approaches to modify the polymer nanocomposites by various inorganic substances
can lead to a huge number of additional functionalities which are increasingly demanded by the textile industries. In the
present work, zinc oxide nanoparticles were prepared by wet chemical method and ZnO–PMMA nanocomposites were prepared by dispersing
the ZnO nanoparticles in solution of poly(methylmethacrylate) (PMMA) and applied on polyamide fabrics by padding. The aims
are to impart superhydrophobicity and UV protection function to the polyamide textile surface and the functional properties
of coated fabrics were studied. The nanofinished polyamide fabrics showed superhydrophobicity of about 163°. The results also
showed that the impregnation of fabrics with ZnO–PMMA nanofinishings also enhanced the protection of polyamide fabrics against
UV radiation. 相似文献
14.
Motoyuki Sugano Yuusuke Iwabuchi Tohru Watanabe Jun Kajita Kohji Iwata Katsumi Hirano 《Clean Technologies and Environmental Policy》2010,12(6):653-659
The variations in the chemical characteristics of asphalt constituents and styrene–butadiene–styrene triblock copolymer (SBS)
in the polymer modified asphalt (MA) during degradation process should be clarified to design the effective recycle method
of MA. In this study, the chemical characteristics of MA during thermal degradation process were studied in detail. The effects
of the period of thermal degradation of MA, the content of asphaltene constituent in MA and the kind of substrate instead
of the straight asphalt were discussed from the yield and thermogravimetry (TG) curves of four constituents in MA and the
molecular weight distribution of SBS. As a result, the yield of polar constituent (asphaltene) increased gradually with decomposition
of SBS during thermal degradation of MA. Decomposition of SBS was enhanced by the low molecular weight substrate, such as
aromatic oil. On the other hand, decomposition of SBS was inhibited by MA of high asphaltene content. 相似文献
15.
Mehmet Dasdemir Benoit Maze Nagendra Anantharamaiah Behnam Pourdeyhimi 《Journal of Materials Science》2012,47(16):5955-5969
In this study, we investigated the effect of polymer type, composition, and interface on the structural and mechanical properties of core–sheath type bicomponent nonwoven fibers. These fibers were produced using poly(ethylene terephthalate)/polyethylene (PET/PE), polyamide 6/polyethylene (PA6/PE), polyamide 6/polypropylene (PA6/PP), polypropylene/polyethylene (PP/PE) polymer configurations at varying compositions. The crystallinity, crystalline structure, and thermal behavior of each component in bicomponent fibers were studied and compared with their homocomponent counterparts. We found that the fiber structure of the core component was enhanced in PET/PE, PA6/PE, and PA6/PP whereas that of the sheath component was degraded in all polymer combinations compared to corresponding single component fibers. The degrees of these changes were also shown to be composition dependent. These results were attributed to the mutual interaction between two components and its effect on the thermal and stress histories experienced by polymers during bicomponent fiber spinning. For the interface study, the polymer–polymer compatibility and the interfacial adhesion for the laminates of corresponding polymeric films were determined. It was shown that PP/PE was the most compatible polymer pairing with the highest interfacial adhesion value. On the other hand, PET/PE was found to be the most incompatible polymer pairings followed by PA6/PP and PA6/PE. Accordingly, the tensile strength values of the bicomponent fibers deviated from the theoretically estimated values depending on core–sheath compatibility. Thus, while PP/PE yielded a higher tensile strength value than estimated, other polymer combinations showed lower values in accordance with their degree of incompatibility and interfacial adhesion. These results unveiled the direct relation between interface and tensile response of the bicomponent fiber. 相似文献
16.
Sok Won Kim Jaeran Lee Bo-Min Jeon Eun Jung Sang Hyun Lee Kweon Ho Kang Kwon Taek Lim 《International Journal of Thermophysics》2009,30(4):1234-1241
Lead–tin (Pb–Sn) alloys are the dominant solders used for electronic packaging because of their low cost and superior properties
required for interconnecting electronic components. However, increasing environmental and health concerns over the toxicity
of lead, combined with global legislation to limit the use of Pb in manufactured products, have led to extensive research
and development studies of lead-free solders. The Sn–Ag–Cu ternary eutectic alloy is considered to be one of the promising
alternatives. Except for thermal properties, much research on several properties of Sn–Ag–Cu alloy has been performed. In
this study, five Sn–xAg–0.5Cu alloys with variations of Ag content x of 1.0 mass%, 2.5 mass%, 3.0 mass%, 3.5 mass%, and 4.0 mass% were prepared, and their thermal diffusivity and specific heat
were measured from room temperature to 150 °C, and the thermal conductivity was calculated using the measured thermal diffusivity,
specific heat, and density values. Also, the linear thermal expansion was measured from room temperature to 170 °C. The results
show that Sn–3.5Ag–0.5Cu is the best candidate because it has a maximum thermal conductivity and a low thermal expansion,
which are the ideal conditions to be a proper packaging alloy for effective cooling and thermostability. 相似文献
17.
The non-isothermal and isothermal degradation behaviors and kinetics of poly(L-lactide) (PLLA) were studied by using thermogravimetry analysis (TGA) in nitrogen and air atmosphere, respectively. At lower heating rate ((5–10)°C/min), PLLA starts to decompose in air at lower temperature than those in nitrogen atmosphere; however, at higher heating rate ((20–40)°C/min), the starting decomposition temperature in air are similar to those in nitrogen atmosphere, not only showing that PLLA has better thermal stability in nitrogen than in air atmosphere, but also suggesting that the faster heating rate will decrease the decomposition of PLLA in thermal processing. Whether in air or in nitrogen atmosphere, the decomposition of PLLA has only one-stage degradation with a first-order decomposed reaction, suggesting that the molecular chains of PLLA have the similar decomposed kinetics. The average apparent activation energy of non-isothermal thermal degradation (Ēnon) calculated by Ozawa theory are 231.7kJ·mol−1 in air and 181.6kJ·mol−1 in nitrogen; while the average apparent activation energy of isothermal degradation (Ēiso) calculated by Flynn method are 144.0kJ·mol−1 in air and 129.2kJ·mol−1 in nitrogen, also suggesting that PLLA is easier to decompose in air than in nitrogen. Moreover, the decomposed products of PLLA are also investigated by using thermogravimetry-differential scanning calorimetry-mass spectrometry (TG-DSC-MS). In air atmosphere the volatilization products are more complex than those in nitrogen because the oxidation reaction occurring produces some oxides groups. 相似文献
18.
L. I. Gracheva 《Strength of Materials》2007,39(3):307-319
We study the results of experimental investigation of the thermal deformation of carbonized carbon fiber-reinforced plastics
used as a heat-shielding material for aircrafts and shuttle spacecrafts. It is shown that, in the process of thermal cycling
of laminated carbon-carbon composite materials with chaotic or three-dimensional reinforcement, the degree of thermal expansion
increases independently of the gaseous environment of testing up to a certain number (4–5) of heating cycles. As the number
of thermal cycles increases, the thermal strains induced in the materials gradually decrease due to the structural changes
in the matrix, fiber, and at the interfaces of materials in the composite.
__________
Translated from Problemy Prochnosti, No. 3, pp. 118–133, May–June, 2007. 相似文献
19.
Experimental data for carbon–carbon constituent materials are combined with a three-dimensional stationary heat-transfer finite element analysis to compute the average transverse and longitudinal thermal conductivities in carbon–carbon composites. Particular attention is given in elucidating the roles of various micro-structural defects such as de-bonded fiber/matrix interfaces, cracks and voids on thermal conductivity in these materials. In addition, the effect of the fiber precursor material is explored by analyzing PAN-based and pitch-based carbon fibers, both in the same type pitch-based carbon matrix. The finite element analysis is carried out at two distinct length scales: (a) a micro scale comparable with the diameter of carbon fibers and (b) a macro scale comparable with the thickness of carbon–carbon composite structures used in the thermal protection systems for space vehicles. The results obtain at room temperature are quite consistent with their experimental counterparts. At high temperatures, the model predicts that the contributions of gas-phase conduction and radiation within the micro-structural defects can significantly increase the transverse thermal conductivity of the carbon–carbon composites. 相似文献
20.
The interaction of alloys based on SmCo5 with hydrogen is studied by the methods of differential thermal and X-ray phase diffraction analyses under initial pressures
of hydrogen of 200, 300, 400, 500, and 650 kPa at temperatures of up to 1223°K. The hydride of the alloy is formed up to a
temperature of 343°K. Within the temperature ranges 388–408°K and 488–523°K, hydrogen is released from the hydrides of phases
of the alloy. Within the temperature range 823–863°K, the alloy partially disproportionates into Sm Hx and Co. At 1008–1053°K, SmHx undergoes partial decomposition and the SmCo5 and Sm2Co17 phases are detected. The Co, SmCo5, and Sm2Co17 phases exist at temperatures above 1168–1188°K. The compositions of the phases depend on the duration of interaction of the
alloy with hydrogen.
__________
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 1, pp. 94–98, January–February, 2007. 相似文献